1. Field of the Invention
This invention relates to theatrical safety curtain devices. The invention relates more particularly to an improved apparatus for automatically lowering a fire curtain in a theater.
2. Description of the Prior Art
Fire safety devices which are utilized in theaters include a fire curtain which is arranged to establish a fire resistant barrier between a backstage of the theater and the audience section. The fire curtain arrangement generally includes a curtain frame and fire resistant fabric, such as asbestos, which is suspended aloft above a proscenium opening, and, a means for automatically lowering the fire curtain to close the proscenium opening upon detection of combustion. A fire curtain is of considerable weight and in order to facilitate raising and lowering of the curtain for installation and maintenance, a counterbalance arrangement is provided. In general, the curtain is suspended from a plurality of wire ropes each of which extends vertically from the curtain to a block mounted aloft, to a rotatable traction head block, and to a counterbalance weight which is coupled to an opposite end of the wire rope. The weight of the counterbalance is selected to be somewhat less than the weight of the safety curtain. In this mechanically unbalanced arrangement, the curtain would descend. However, engagement between the wire ropes and the traction head block establishes a frictional force which resists slippage between the wire rope and head block and inhibits descent of the curtain. Rotation of the head block is inhibited by virtue of resistive frictional forces which are applied to the head block from an electric drive and speed reducing means through a mechanical coupling. Upon energization of the electric drive means, the head block is rotated in the desired direction to case the desired ascent or descent of the curtain during installation and maintenance procedures.
The safety curtain is normally suspended aloft and in order that it may automatically and rapidly descend upon the occurrence of combustion, a sensing system consisting of a cut wire having a number of fusible links formed in the wire is provided and is positioned about the proscenium opening. The cut wire extends to the mechanical coupling of the traction head block and the electric drive and speed reducing means. Upon occurrence of combustion, a fusible link will melt thereby severing the cut wire to initiate interruption of mechanical coupling between the electric drive and the traction head block. This removes the restraining force on the head block and permits the curtain to descend.
Prior safety curtain arrangements have utilized a coupling between the electric drive and the head block which includes a clutch. The clutch arrangement however has required application of a relatively large actuating force to the clutch for interrupting mechanical coupling and enabling curtain descent. A counterbalance arrangement has been provided for aiding in actuation of the clutch decoupling. However, the relatively large clutch actuating force thus provided needs to be carefully balanced to assure both freedom from premature decoupling while maintaining sensitivity to combustion. It has been observed that the required release force for actuating the clutch, because of the construction of the clutch, at times exhibits a disadvantageous tendency to vary in magnitude and can exceed the force designed to be applied thereto by the relatively sensitive balanced cut wire arrangement. This is particularly true when frequent checking and maintenance of the curtain system is not practiced and the reliability of the system is decreased. Alternatively, theater personnel must regularly and frequently operate the safety curtain apparatus in order to verify its reliability.